FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to fuel assemblies and, more particularly, to a fuel assembly which is suitable for use in a boiling water reactor and which has ferrule spacers of round-cell type.
Generally, the fuel assembly is provided with a plurality of fuel rods and a single water rod, and upper and lower tie plates which hold or retain both ends of these rods. Further, these rods are supported with their spacings retained by spacers. The fuel assembly is accommodated or received within a channel box.
As a spacer which is used in the fuel assembly of this kind, there is a spacer disclosed in U.S. Pat. No. 5,173,252. The spacer is provided with a plurality of cells into which the fuel rods are respectively inserted, and a plurality of loop springs which are held or retained by pairs of adjacent cells, respectively. Each of the loop springs is provided with a pair of resilient members which radially urge the fuel rods and a pair of connecting members which connect axial ends of the resilient members to each other. The connecting members have passages through which coolant flows axially.
In the conventional spacers, the passage in the connecting member of the loop spring is defined by a closed circumferential wall. Moreover, a thickness of peripheral walls is uniform. For this reason, if the loop springs are arranged within flow of the coolant, fluctuation of flow of the coolant causes the loop springs to be inclined in opposite directions around an axis which passes through abutting points between the fuel rods and the resilient members. Thus, repeated sliding movement occurs between the fuel rods and the resilient members of the loop springs so that both of them sustain damage.